The present invention pertains generally to lasers and more particularly to free electron lasers.
Since the concept of the first laser was demonstrated, the scientific community has had a great interest in the development of a high power laser which could be continuously tuned over a wide range of frequencies. A high power laser which could be tuned in this manner would have great utility for industrial chemistry applications to supply energy to specific reactions. For example, such a laser could be used as a source to clean exhaust gases from combustion by selectively decomposing noxious substances. Similarly, feedstocks could be purified for chemical processes by selective destruction of contaminants. For example, coal gasification can be accomplished by using a high power continuously tunable laser to remove impurities which would adversely affect catalysts used in the gasification process.
With the advent of the gaseous molecular laser, high powers have been achieved. However, gaseous molecular lasers are incapable of being tuned over more than a very restricted range of frequencies and produce only a specific set of frequencies depending upon the gaseous lasing medium.
The concept of extracting coherent optical radiation from a stream of relativistic electrons, i.e., the free electron laser, was first described by J. M. J. Madey, of Stanford, in 1971. Several years ago, J. M. J. Madey et al. reported lasing action from stimulated Bremsstrahlung from the Stanford Superconducting Accelerator as reported in Phys. Rev. Letts. 38, 892 (1977). A collaborative effort by the Columbia University Laboratory and the Naval Research Laboratory has produced a laser based on stimulated Raman scattering by free electrons as reported by D. B. McDermott et al., Phys. Rev. Letts. 41, 1368 (1978). The report of these results of the "free electron laser" has caused much excitement in the scientific community since it is possible that free electron lasers will be able to produce exceedingly high powers at low cost and continuously tunable frequency.
In addition to the continuously tunable frequency and potentially high output powers obtainable from the free electron laser, the free electron laser has the added advantage of the absence of a lasing medium, such as a fluid, glass, or gaseous molecules, which tend to limit the power and spatial resolution by nonlinear optical effects in the lasing medium.
However, to date, only low efficiencies have been demonstrated or envisioned by the various free electron laser systems proposed having wavelengths shorter than the near ir. Consequently, tremendous energy is required to operate free electron lasers at short wavelengths (e.g., less than approximately 1 micron) and high output powers, necessarily affecting utilization of these devices in industrial applications and other areas.
The dc accelerator/decelerator concept described by L. R. Elias, Phys. Rev. Letts. 42, 977 (1979) does achieve good efficiencies at longer wavelengths (e.g., less than approximately 10 microns). However, many industrial applications as well as other applications require shorter wavelengths for operation.
U.S. patent application Ser. No. 90,846 filed Nov. 2, 1979 by Charles A. Brau, Donald A. Swenson, and Thomas J. Boyd, Jr. entitled "RF Feedback Free Electron Laser," now U.S. Pat. No. 4,287,488 issued Sept. 1, 1981, discloses a configuration using rf coupled accelerating and decelerating structures having dual electron beams which is capable of producing high efficiencies at shorter wavelengths. However, the use of dual electron beams and the multiple structure cavity required in the above disclosed application results in a device which is somewhat complex to implement.